Tracking system tracker unit

ABSTRACT

Apparatus and methods processing the video signal of a television camera sensor into a tracking error correction signal form used to control the viewing axis of the television camera sensor in tracking alignment with respect to a detected target. A pre-gate or post-gate extension, or both, is combined with the basic tracker unit tracking gate pulse to develop improved tracking control in directions at right angles to the television camera sensor direction of line scanning.

Z,5@ -ZO3-LT AU Z56 tX Z+-73 XR 397291582 United States Patent 1 [1113,729,582

Deye et al. 1 Apr. 24, 1973 [54] TRACKING SYSTEM TRACKER UNIT 2,970,1871/1961 Hinton ..l78/6.8

3,320,360 5 1967 Th ..l78 6.8 {75] Inventors: Neil S. Deye;'Ricl1ard B.Kuhn, both ompson of Columbus Ohm Primary Examiner-Benjamin A. Borchelt[73] Assignee: North American Rockwell Corpora- Assistant Examiner--S.C. Buczinski tion Att0rneyWilliam R. Lane and Daniel H. Dunbar [22]Filed: Jan. 18, 1967 Relaied Application Dam Apparatus and methodsprocessing the video signal of [62] Division of sen No 403 396 Oct. I21964 a television camera sensor into a tracking error correction signalform used to control the viewing axis of {52 us. Cl ..l78/6.8, 250/203cr, l78/DlG. 21 the television camera Sensor in tracking alignment [5 1]Int. Cl. ..H04n 3/00 with respect to a detected target A D -8 or P i[58] Field of Search ..178/6.8, DIG. 21; g extension, both. i5 Combinedwith the basic 250/203 CT tracker unit tracking gate pulse to developimproved tracking control in directions at right angles to the [56]References Cited television camera sensor direction of line scanning.

UNITED STATES PATENTS 12 Claims, 13 Drawing Figures 2,764,698 9/1956Knight ..250/203 X TELEVISION z- H 9 i ll i TRACKER PL'ATFoRM OPERATORAND DR'VE COMMAND pow 7 CONTROLS SUPPLY DEFLECTION AND T -SYNCHRONIZ|NGCIRCUITS Patented April 24, 1973 3,729,582

3 Sheets-Sheet 1 4 IO N/. 1 TELEVISION gag V'DEO OA'MERA --PROcEss|Ne -4f a I SECTION l 1 I L O I 12 TRACKER 2| 3 i '1' VERTICAL"- HORIZONTALPLATFORM OPERATOR LOGIC LOGIC AND 1 SECTION SECTION L- SUPPLY jl TTfIlII-I T i: L l I i I I! (if I'll m7.

LS l l (b) A T .m.

Patented April 24, 1973 3 Sheets-Sheet 5 CROSS-REFERENCE Thisapplication is a Divisional application of copending application Ser.No. 403,396, filed Oct. 12, 1964.

SUMMARY OF THE INVENTION The tracking system tracker unit of the instantinvention is comprised of apparatus that develops tracking errorcorrection signals for controlling the television camera sensor viewingaxis in both azimuthal and elevational tracking alignment with aselected target indirectly through the tracker unit support platform.The desired azimuthal tracking error correction signal is derived fromthe coincidence of: elevational tracking, desired azimuthal alignmentmanifested by the time position of a comparatively narrow basicazimuthal tracking gate pulse, and detected target edge deviation fromtracking alignment. The azimuthal tracking gate pulse is in effectdriven away from any detected singularly coincident target edge andtoward the target interior; support platform correction is correlatedwith respect thereto. The desired elevational tracking error correctionsignal is derived from the coincidence of: azimuthal tracking, desiredelevational alignment manifested by the time position of an elevationaltracking gate pulse, and detected target edge deviation from trackingalignment. The detected target edge that develops the coincidencerelation for azimuthal tracking correction normally is positioned justoutside or just into the basic tracking gate pulse during trackingalignment. In accordance with our invention, a pre-gate or post-gateextension (or both) is added to the azimuthal tracking gate pulse and isused to indicate azimuthal tracking when establishing coincidence forthe elevational tracking error correction signal derivation. Suchextension functions to significantly minimize or eliminate thelikelihood of loss of target lock-on during automatic tracking by thetracking system tracker unit.

DRAWING DESCRIPTION FIG. I is a functional block diagram of a trackingsystem of the type which may advantageously incorporate a tracker unithaving the features of this invention;

FIG. 2 is a functional block diagram of the construction that is basicto the type of tracker unit to which this invention applies;

FIG. 3 is an elevational view of one suitable form of the monitor unitand the command controls unit shown as separate functional blocks inFIG. 1;

FIG. 4 is a combined sectional view and functional block diagram of oneform of television camera unit that has been used with the embodimentsof a tracker unit shown schematically in FIG. ,5;

FIG. 5 is a schematic diagram of a tracker unit having a preferredembodiment of the apparatus of this invention incorporated therein;

FIG. 6 details various coincidence relations that do or may existbetween edge marker pulses of a selected target and the basic horizontaltracking gate pulse utilized in the FIG. 5 tracker unit embodiment;

FIGS. 7 through 13 detail key waveforms that appear at noted pointswithin the tracker unit shown in FIG. 5 during tracking system automatictracking operation.

DETAILED DESCRIPTION The type of tracking system which this invention isbroadly concerned with is illustrated generally by the functional blockdiagram of FIG. 1. Such tracking system is referenced as 10 and isbasically comprised of an optical sensor in the form of televisioncamera unit 11, a platform and drive unit 12, and a tracker unit 13. Theplatform portion of unit 12 serves to support television camera 11;during operation of system 10 in its automatic tracking mode the driveportion of unit 12 serves to move the platform and connected camera unit11 in tracking relation to the relatively movable target T positionedwithin the field of view designated 14. Tracker unit 13 regulatestracking movement of platform and drive unit 12 and couples that unit totelevision camera 11 in a feedback control relation. In addition, system10 includes a monitor unit 15 which takes the form of a typicalmonochrome television picture tube and which is used to present a visualdisplay of the general tracking problem viewed by the optical sensor andan indication of system tracking alignment. A human operator providesthe link which exists between monitor unit 15 and the command controlsfunction designated 16. The operator is normally responsible foraccomplishing such command functions as activating the system, selectingthe system mode of operation (scanning or automatic tracking), selectingthe target if choice is involved, and obtaining acquisition of theselected target in the system tracking reticle prior to locking-on forautomatic system tracking. A power supply 17 of conventional form istypically included in system 10 to provide the preferred electricalenergy for system operation.

FIG. 4 is included in the drawings to provide a schematic illustrationof a type of television camera unit that has been utilized in a trackingsystem 10 which incorporated a tracker unit having the features of thisinvention. Such television camera unit is referenced generally as 22 andis basically comprised of a lens system 23, a camera tube 24,conventional video signal circuits 25, and conventional deflection andsynchronizing circuits 26. For the purpose of this invention a specificform of television camera tube is not necessary; however, a vidicon-typecamera tube such as is shown as component 24 of FIG. 4 has been utilizedas the optical sensor portion of a tracking system having an actualembodiment of this invention. The specific vidicon-type camera tube 24had a signal electrode photoconductive layer with a X 5a" format. Thevideo signal circuits 25 and the deflection and synchronizing circuits26 associated with the actually used unit 22 operated to produce astandard l-volt television camera output video signal (A) and acomposite horizontal and vertical synchronization signal (C) with afield repetition rate of 60 cycles per second. Since closed-loopcircuits are normally used, it is not required that signals A and C becombined for transmission. Such signals, as used, did produce a standardraster comprised of 525 lines; interlacing of separate field frames canbe used but is entirely optional insofar as the hereinafter-claimedinvention is concerned. In

addition, the video signal A of the actually used FIG. 4 arrangementincluded blanking pulses in correlated relation to the signal Chorizontal and vertical synchronization information. Equalization pulsesassociated with the conventional horizontal and vertical synchronizationsignal produced by circuits 26 are not necessary to operation of thetracking system; also it is generally preferred that the verticalsynchronization pulses contained within signal C be non-serrated.

FIG. 2 illustrates the functional block construction of a tracker unitwhich is designated 18 and which may have any one of the severalspecific embodiments detailed in the drawings and in the followingdescription; such construction may be advantageously utilized as thetracker unit for tracking system of the type disclosed generally byFIG. 1. Tracker unit 18 is essentially comprised of a video processingsection 19, a horizontal logic section 20, and a vertical logic section21. Basically, tracker unit 18 receives the output signals of televisioncamera unit 11 (e.g., signals A and C of the FIG. 4 means) and bypreferred apparatus (circuit means) and information processing methodsderives two output signals that may conveniently be used to controlazimuthal and elevational movement of unit 12 (and camera 11) during theautomatic tracking mode of system operation. One such output signal(X,,) is basically produced by horizontal logic section 20 and is anerror correction signal for automatic tracking in an azimuth sense; theother output signal (Y,,) is basically produced by vertical logicsection 21 and is an error correction signal for automatic tracking inan elevation sense. Particular schematic arrangements which are used tocomprise the hereinafter described preferred embodiments of tracker unit18 are disclosed in connection with FIG. of the drawings.

Several general comments are desirable with respect to the tracker unitdetails in the drawings. First, most of the included circuits (e.g.,video signal amplifiers 31, 32, synchronizing signal amplifier 33, mixer34, and the like) are or can be conventional in both function andconstruction and are sufficiently well known so that a functional blockdescription is adequate for disclosure purposes; details regarding theirconstruction are not shown in the drawings. Those circuits which arefundamental to operation of the tracker unit described herein and whichgenerally are not clearly understood by a functional description aloneare further detailed as to a suitable specific form in theabove-referenced copending US. Pat. application Ser. No. 403,396. Inconsidering the following description it should also be kept in mindthat the disclosed embodiment ofa tracker unit is basically adigital-type system that processes information in pulse form; the videosignal inputs to, and the tracking error correction signal outputs from,the tracker units, however, are essentially analog in form. Generally,and unless otherwise noted, it is preferred for uniformity purposes thatthe various disclosed pulse circuits be triggered and fired by detectedpositive changes in the voltage shape of a received pulse. Accordingly,it often is necessary to employ various inverter circuits (e.g., theinverter circuit 46 of FIG. 5) to key triggering actions to the leadingedge of negative pulses or the trailing edge of positive pulses.Frequent reference is made in the drawings to a circuit identified as aone-shot (e.g., circuit 29, 45, etc.). Such circuit is better describedtechnically as a monostable multivibrator circuit. In those instanceswhere the monostable multivibrator circuit employed requires aparticular operating duration characteristic, such is indicated in thedescription. Generally speaking, the basic coupling of individualcircuits to a power supply (8+ or B) or to a necessary ground orreference value voltage is well-understood and is not always shown;similarly usable signal levels are not specified herein. The trackerunit embodiment of the drawings is described in operating relation to atelevision camera video signal wherein increasing signal voltages arecaused by increasing image brightness; by polarity reversal techniquesthe tracker unit can be made to operate equally well using or receivinga television video signal based on a negative transmission method.

Also, unless otherwise noted, the following description refers tonegative and positive voltage values and such polarities have meaningwith respect to a basic viewing reference. Targets positioned at thecenter of the system tracking reticle (and also at the center of themonitor of video signal raster) require zero tracking correction andproduce zero position voltages and zero value correction signals.Targets viewed in or moved to the raster left or top portions establishpositive voltage signals of proportionally increasing value to indicateposition location or tracking correction. Conversely, targets viewed inor moved to the raster right or bottom portions are tracked usingcomparatively negative voltage values to indicate position or nature ofcorrection required. Such polarities are particularly important withrespect to the output X, and Y, signals of the tracker unit.

Referring to the embodiment of tracker unit 18 shown in FIG. 5, thebasic function of forming marker pulses associated with a detectedtarget edge deviation from tracking alignment is accomplished by videoprocessor circuit 27 and by one-shots 29 and 30 therein. One-shot 81(and cooperating inventer 82) function to establish the delay requiredfor a highly desired false trailing edge" marker pulse for each detectedchange in the selected class of contrast changes detected by circuit 27.Such false trailing edge pulse is formed by one-shot 30 and is importantfrom a standpoint of system performance in situations where the targetedge separation otherwise is great with respect to the basic trackinggate pulse duration. The signals A and C that are received fromtelevision camera unit 11 may e amplified, as by the adjunct amplifiercircuits 31, 32, and 33. In addition, a mixer circuit 34 may beincorporated in video processing section 19 for use in developinginformation to be utilized in monitor unit 15 to display an indicationof tracking system tracking alignment. The basic output signals of videoprocessing section 19 are constant marker pulse signals designated +Eand -E. Normally, E marker pulses are associated with decreasing videosignal voltages including the leading edge (FIG. 9) ofa selectedcomparatively dark target.

Basically, video processor circuit 27 receives an amplifier video signalA and by differentiating operations detects all increases or decreasesin signal voltage which occur within each horizontal line of camerafield-of-view scan. By use of a suitably selected circuit time constantvalue, circuit 27 is made to provide positive and negative edge pulses D(FIG. 9) corresponding respectively to increases and decreases detectedin the voltage of video signal A. A suitable transistorized circuit foraccomplishing the differentiating function is shown in FIG. 10 of theabove-identified co-pending parent application. Those edge pulses whichdesignate decreasing voltage slopes (FIG. 9) are conducted by channel 36after inversion to one-shot circuit 29 where a squaring and stretchingfunction is accomplished. Similarly, those edge pulses also triggerone'shot 81 whose output, after inversion by element 82, initiatesone-shot circuit 30 to in effect accomplish a similar squaring andstretching function. In an actual embodiment of the tracker unit of FIG.5 it was found desirable that the pulse durations obtained by one-shots29 and 30 should be approximately l/l0 to 1/5 of the video signalhorizontal scan time duration that indicates the minimum image of theselected target projected on the photoconductive layer format of cameratube 24 during automatic system tracking; the output pulse durationsthat were actually developed were each 0.3 microseconds. In selectingthe individual components for one-shot circuit 81, it is preferred thatthe circuit output signal have a time duration just a little longer thanthe duration of the basic horizontal tracking gate pulse developed byone-shot circuit 45; thus, in the actual embodiment of the FIG. 5tracker unit arrangement, one-shot circuit 81 was provided with a l.5microsecond width in relation to a 1.0 microsecond basic horizontaltracking gate pulse width. The output pulse signals of one-shots 29 and30 are designated as E and +E, respectively, in the remaining portion ofthis description. Such one-shot output signals are hereinafterfrequently referred to as marker pulses and are the previouslyreferenced basic output signal pulses of video processor section 18.

It is required that the operation of horizontal and vertical logicsections and 21 be synchronized with the tracking problem informationsensed optically by camera unit 11 and transmitted in video signal A.For this reason, tracker unit 18 of FIG. 5 is provided with asynchronization circuit that in one form is essentially comprised ofone-shot circuits 40 and 41, intermediate pulse inverter circuit 42, andAND gate circuit 43. Such synchronization circuit is located in section20 of the FIG. 5 arrangement only as a matter of convenience. One-shotcircuit 40 is triggered by the leading edge of each synchronizationpulse comprising composite signal C and produces a positive pulse outputsignal C, having a time duration that is at least greater than the pulsewidth of any horizontal synchronization pulse in composite signal C butthat is appreciably less than the time duration of one video signalscan-line. In an actual embodiment of the FIG. 5 arrangement, a timeduration of approximately onehalf scan-line (e.g., 30 microseconds) hasbeen found suitable for output pulse signal C Such signal C, is invertedby circuit 42 so that the decreasing voltage trailing edge of C, ineffect triggers one-shot circuit 41 to thereby cause circuit 41 tocreate a pulse signal C, that serves a triggering function and thatexists only during the absence of a horizontal synchronization pulse. Acomparatively short time duration (e.g., 2 microseconds) for such outputpulse signal C, has proven adequate for at least one known tracker unitapplication. AND gate circuit 43 receives all pulses of compositesynchronization signal C and also all trigger pulse signals C, fromone-shot circuit 41. Such trigger pulse C, is gated through AND gate 43only when it is time coincident with a vertical synchronization pulse.See FIG. 9. The trigger pulse gated through AND gate circuit 43 also isreferenced as signal C,. It should be noted that signal C issynchronized with the vertical synchronizing pulse but has a slight timelag with respect to its leading edge; such delay is not at alldetrimental to the operation of vertical logic section 21.

A basic horizontal (azimuthal) tracking gate pulse signal G (FIG. 7)having a controlled time position in each raster scanline is developedin horizontal logic section 20 essentially by means of controllablemonostable multivibrator circuit 44 and one-shot circuit 45. Details ofa suitable construction for circuit 44, also referred to as a horizontalposition voltage to pulse width converter circuit, are provided in thedrawings and description of previously identified application Ser. No.403,396. Such circuit is essentially a time delay circuit that istriggered by a positive-going voltage change in the leading edge of eachpulse C generated by oneshot circuit 40; such leading edges alsocorrespond to the leading edges of the horizontal synchronization pulsesin signal C. The output signal F of circuit 44 is a negative-going pulsewhose time duration from start is proportional to the magnitude offeedback analogue voltage signal X, which is developed by section 20 asa whole. One-shot circuit 45 develops a positive output pulse G whichhas a short time duration and which is the hereinbefore referred tobasic horizontal tracking gate pulse. Inverter circuits 46 and 47, whichcircuits may comprise a dual inverter circuit module, are utilized inpart to condition horizontal tracking gate pulse G for use in otherportions of horizontal logic section 20.

Horizontal logic section 20 in the FIG. 5 arrangement also develops aconcurrence gate pulse for use in vertical logic section 21, such gatepulse (U) being a time-extended version of the basic horizontal trackinggate pulse G. The components for accomplishing the difference inconstruction are essentially one-shot circuit 83, one-shot circuit 84,and the flip-flop circuit comprised of cooperating inverter circuits 86and 87. In normal inverter applications the two input terminals of eachsection to a typical dual inverter circuit module are joined together;in flip-flop current applications,

however, the input terminals remain separate.

One-shot circuits 83 and 84 each provide an extension at one side of thebasic horizontal tracking gate pulse G. The output pulse S of one'shotcircuit 83, is of comparatively short duration and leads basichorizontal tracking gate pulse G; in inverted form the trailing edge ofsignal S triggers one-shot circuit 45. See FIG. 7. The basic horizontaltracking gate pulse G is inverted by circuit 46 and its trailing edgetriggers one-shot circuit 84 to produce output pulse T. Pulse T is alsoof comparatively short duration and trails the trailing edge of pulse G.In one embodiment of the detailed tracker unit, and in the case of pulseS, pulse T provided an 0.5 microsecond extension to the adjacent edge ofbasic horizontal tracking gate pulse G. By means of flip-flop circuit85, a positive-going extended horizontal gate pulse U is developed fromS, G, and T signal pulse components for vertical logic section 21. Theflip-flop circuit is utilized rather than an AND gate so as to eliminateany discontinuity which otherwise would or could appear in the compositeextended horizontal gate pulse.

The detection of a horizontal tracking alignment error is accomplishedessentially by paired but independent AND gates 48 and 49. Detailsregarding a typical satisfactory construction for the AND gates used inthe invention are provided in said co-pending application Ser. No.403,396. AND gates 48 and 49 each utilize three input terminals. In eachinstance, one of the input terminals receives the positive-goinghorizontal tracking gate pulse signal G originated in one-shot circuit45 as fully inverted and re-inverted by circuits 46 and 47. Anotherinput terminal of each such AND gate receives pulse signal L developedwithin vertical logic section 21 and correlated to vertical trackingconcurrence. AND gate circuit 48, in the arrangement of FIG. 5, alsoreceives all E edge marker pulse signals produced by one-shot 29 ofvideo processor section 19; similarly, AND gate 49 is arranged toreceive all of the +E edge marker pulse signals developed by one-shotcircuit 30 of video processor section 19. AND gate circuits 48 and 49each function to pass the -E and +E edge marker pulse signals through totrigger or fire oneshot circuits 50 and 51, respectively, wheneversignals G and L are time-coincident therewith. A separate waveformdesignation M is assigned to the passed signals resulting from thedetected time-coincidence. Such signals, which are basically trackingerror detection signals, in turn are preferably extended time-wise byone-shot circuits 50 and 51 to just less than one scan-line period induration (e.g., 60 microseconds) to form the basic horizontal trackingerror pulse signals N developed within tracker unit 18; such signalsexist in either a -N or +N category although each would have anidentical positive-going polarity form. Oneshot circuits and 51 aresimilar to circuit 30 but must each be provided with a fast-recoverycapability (e.g., 0.5 microseconds).

Tracker unit 18 also detects vertical tracking errors and developsrelated correction signals, such being accomplished essentially withinvertical logic section 21. However, the apparatus and informationprocessing methods utilized in section 21 differ somewhat inconstruction and function from the comparable aspects of horizontallogic section 20. The differences essentially relate to use of adifferent form of tracking gate; also, position information concerningthe detected target is derived from horizontal logic section signalsrather than from video processor section 19.

Vertical tracking gate pulse signals having a controlled verticalposition within the vertical extent of the complete raster produced bytelevision camera unit 11 are developed in vertical logic section 21essentially by means of controllable monostable multivibrator circuit 54and one-shot circuits 98 and 99. Circuit 54 is also referred to as avertical position voltage to pulse width converter circuit; it is a timedelay circuit that is triggered by a positive-going voltage change inthe leading edge of each pulse C, passed through AND gate circuit 43.Such leading edge identifies the existence ofa vertical synchronizationpulse within composite signal C. The output signal H of circuit 54 is anegative-going pulse whose time duration from start is proportional tothe voltage of signal Y, developed by section 21 as a measure ofrequired vertical tracking error correction for the system. Output pulseH has a positive-going trailing edge that fires one-shot circuit 96only. Oneshot circuit 98 develops a positive output pulse J having atime duration that constitutes one portion of the basic verticaltracking gate of tracker unit 18. Signal J in one actual embodiment ofthe invention was provided with a time duration of approximately 400microseconds or 6 video signal scan-line periods; stated in anothermanner, signal J in time duration was preferably in the range of N60 to1/125 of the duration of the video signal A field repetition frequency.The pulse signal J output of one-shot circuit 98 is inverted by invertercircuit means 60 so that its trailing edge in effect triggers one-shotcircuit 99. The output signal K of circuit 99 preferably has a form andduration corresponding to the form and duration of signal J produced byone-shot circuit 98. Output pulse signal K then constitutes theremaining portion of the basic vertical (elevational) tracking gate oftracker unit 18. Signals J and K are in effect combined by OR gate 57and form the basic vertical tracking concurrence pulse signal L that isrequired in horizontal logic section 20 on a coincidence basis to gate-E and +E contrast marker pulses through gates 48 and 49. Invertercircuits 61 and 62, like circuit 60, are provided in section 21 todevelop the proper polarity for the indicated pulses at the indicatedstages of signal processing. In this respect, it should be noted that ORgate 57 functions to gate negative pulses; the

output of that gate in turn must be inverted, as by inverter circuit 66,to place the vertical tracking gate pulse in proper polarity conditionfor gates 48 and 49.

In vertical logic section 21 the real and false E contrast marker pulsesdeveloped in video processing section 19 are coincidence gated by pairedout independent vertical tracking gates 93 and 94. Such gating occurswith concurrent extended horizontal tracking gate U and the separatevertical tracking gate portions J and K.

Vertical logic section 21 of the FIG. 5 embodiment also includesconstruction features which serve to stabilize the leading edge portionsof the vertical tracking gate pulses J and K at the raster margin.Basically, the controllable monostable multivibrator circuit designated54 triggers an intermediate one-shot circuit 96 having a duration of atleast one scan-line. The output pulse of circuit 96 AND gates (at ANDgate 97) each coincident pulse of synchronization signal C received fromsynchronizing signal amplifier 33. Thus, one-shot circuit 98 produces aninitial vertical tracking gate pulse J that assuredly is started at theraster left margin in every instance. One-shot circuit 99 develops apositive-going vertical gate pulse K in response to the triggeringaction of the trailing edge of inverted pulse J sourced in circuit 98.Oneshot circuits 98 and 99 are generally similar to previously describedone-shot circuits except that a controllable monostable multivibratorconstruction is employed. Such are triggered by pulses received from ANDgate 97 or inverter circuit 60 but are controlled by synchronizationcircuit 100 to assure that the produced gate pulse is stopped at ascan-line end. Component 101 of synchronization circuit 100 is aZener-type diode. One-shot circuits 102 and 103 are provided in section21 to give essentially one-line duration to the coincidence-passed realand false contrast marker pulses E gated through AND gates 93 and 94.Inverter circuits 67 and 104 are included to develop the proper pulsepolarity for summing circuit 105. Summing circuit 105 and filter circuit106 are preferably of the same construction associated with circuits 91and 92.

The detection of a vertical tracking alignment error is accomplished invertical logic section 21 essentially by paired but independent ANDgates 93 and 94. As in the case of AND gates 48 and 49, such verticalsection gates may use the construction detailed in our co-pending parentapplication. In each instance, one of the input terminals receives asignal from OR gate 95; such signal is essentially made up of E or +Eedge marker pulses. Another input terminal of AND gate 93 receives thevertical tracking gate signal K developed within one-shot circuit 99.AND gate 94, on the other hand, receives the 1 pulse signal portion ofthe basic vertical tracking gate as produced by one-shot 98. The thirdterminal of each such gate (93 or 94) receives the time-extendedhorizontal tracking gate pulse U to establish concurrence withhorizontal or azimuthal tracking. A separate waveform designation P isassigned to the passed pulse signals resulting from the time-coincidenceof a detected target edge manifested by a marker pulse, a verticaltracking gate pulse, and a pulse indicating concurrence with horizontaltracking. Those passed signals (tracking error detection signals) whichare associated with the gating action of one-shot circuit 98 only aregiven a P designation; those vertical tracking error detection signalswhich are developed through time-coincidence with the vertical trackinggate pulse established by one-shot circuit 99 are designated as +P.Time-wise in each raster, +P pulses will normally occur after thedeveloped P pulses.

The remaining portions of logic section 20 and 21 comprise a summingcircuit 91 (or 105), a filter circuit 92 (or 106), and an integratorcircuit 71 (or 72) as shown in FIG. 5. Such additional circuitsessentially function to develop appropriate tracking error correctionsignals (X, or Y,,) for controlling movement of the tracking systemsensor in tracking relation to moving or movable target T. Such trackingerror signals, which are basically in DC voltage analog form, also areprovided as feedback signal inputs to controllable monostablemultivibrator circuits 44 and 54. Detailed construction of particularcircuits for accomplishing the functions of circuits 91, 92, and 71 areprovided in the referenced co-pending parent application.

Summing circuit 91 functions to add the inverted N and +N tracking errorpulses which appear at any instant within horizontal logic section 20during operation of the tracker unit. The output signal of cummingcircuit 91 is designated 0; in the case of circuit 105, the outputsignal is identified by the reference letter R. During precise trackingalignment the difference of -N and +N signals seen by circuits 92 and 71is essentially zero. However, in either case when there is trackingmisalignment a sequence of N or +N pulses are present in the rastermakeup and does cause error correction signals to be developed in thesubsequent portion of the tracker unit. (See FIGS. and 13 for specificexamples.) In the case of summing circuit 105,

and because of the use of sequenced gates J and K, the input trackingerror signals P and inverted +P are entirely non-coincident. Filtercircuits 92 and 106 are provided in the invention so as to essentiallyaverage out or smooth the pulsed output signals 0 and R so as to be inusable form for integrator circuits 71 and 72. Circuits 92 and 102 aresubstantially identical in function but differ in that filter circuit106 must essentially respond to R signals which normally occur insequential groupings. Up to six successive individual pulses maycomprise each such grouping in the case of specific one-shot circuits 98and 99 each having a 400 microsecond output. Integrator circuits 71 and72 respond essentially to the output of circuits 91 and 105; theiroutputs are inverted relative to the polarity of the inputs to thesumming circuits 91 and 105. See FIGS. 11 and 12.

The television picture tube element normally included in monitor unit 15basically receives video signal A and synchronization signal C fordeveloping a conventional visual presentation of the general trackingproblem to be observed by the system operator. The visual displaypresented thereby, however, may be significantly enhanced by otherfeatures of this invention. Such enhancement is accomplished by means ofsumming circuit 75 and by means of the E and +E edge marker pulsesignals developed in circuits 29 and 30. Summing circuit 75 developsso-c alled cross-hair pulse information for presentation on the screenof monitor unit 15. Such cross-hair pulse information develops thepaired horizontal cross-hair lines 77 and the paired vertical cross-hairlines 78 shown in FIG. 3. The rectangular area defined by and locatedwithin the intersection of cross-hair lines 77 and 78 comprise thetracker unit 18 reticle. The cross-hair pulse information is developedin circuit 75 essentially by difi'erentiator sub-circuits that detectnegative-going voltage changes in the leading and trailing edges of theappropriate gate pulses. More specifically, one input terminal ofcircuit 75 receives signal G after a single inversion and detects itsleading edge; another input terminal of circuit 75 receives pulse Gafter a double inversion by circuits 46 and 47 and detects itsnegativegoing trailing edge. Such detected edges comprise, afterinversion and mixing, the cross-hair pulses that form dark cross-hairlines 78. In a similar manner, signals J (after inversion by circuit 60)and K are conducted to summing circuit 75 where their leading andtrailing edges, respectively, are detected. The differentiated detectedleading and trailing edges of the vertical gate pulses are afterwardsintroduced into monitor unit 15 to comprise horizontal cross-hairs 77.

This display developed for monitor unit 15 may also be enhanced byappropriate use of edge marker pulses E and +15 as follows. Mixercircuit 34 can function to gate those edge (contrast change) markerpulses which are time-coincident with tracking gate edge pulsesdeveloped in summing circuit 75 and amplify such passed pulses forpresentation in the picture tube of monitor unit 15. The so-gated andso-amplified marker pulses give a display indication to the operatorthat tracker unit 18 is actually following the selected and displayedtarget contained within video signal A.

FIG. 6 illustrates various coincidence relations that exist as betweenedge marker pulses associated with a selected target and the basichorizontal tracking gate pulse G. In an earlier embodiment of trackerunit 13 the E and +E edge marker pulses associated with the leading andtrailing edges of a selected target were positioned entirely with thehorizontal tracking gate pulse as shown in FIG. 16(a). Although thetracker unit embodiment of FIG. preferably utilizes a pulse relationshipwherein the separation between real and false marker pulses for aselected target is slightly greater than (or just equal to) the basictracking gate pulse duration, the subsequent illustrations of 16(b)through 16( are equally helpful from the standpoint of understanding thesignificance of a non-singularly coincident pulse relationship. If thetarget is moved to the left relative to the viewing axis of the systemoptical sensor, the E leading edge pulse will become coincident with theleading edge of the horizontal tracking gate pulse (FIG. 16(b)).Inasmuch as coincidence is still maintained as between the tracking gatepulse and both target edge marker pulses, no tracking alignment error isdetected. Absence of a target edge marker pulse from within the trackinggate (FIG. 16(0)) causes development of a tracking error signal based onthe singular coincidence of the remaining interiorly positioned targettrailing edge marker pulse. Such error correction signal, as processedthrough summing circuit 91, filter circuit 92, and integrator circuit71, in effect causes the horizontal gate to be repelled away from thecoincident target edge marker pulse and toward the escaped" targetopposite edge (target interior). Relative movement between the targetand the horizontal tracking gate in an opposite direction will causetracking gate conditions corresponding to the relations shown in FIGS.16(d) and 16(e). Sufficient rightward movement of the target willultimately result in only the target leading edge being singularlycoincident with the horizontal tracking gate pulse so as to cause anerror signal indicating a need for tracking correction. See FIG. 16(e).FIG. 160) illustrates the situation which occurs when the selectedtarget in effect outruns the established horizontal tracking gate. Thissituation is commonly referred to as an unlock" situation; it occurswhenever the relative movement between the selected target and theoptical sensor occurs at a rate that exceeds the maximum obtainabletracker unit tracking rate. FIG. 16(g) illustrates the minimum targetedge marker pulse separation which generally may be permitted withrespect to the tracker units described herein. The improved trackingrates which are obtained result chiefly from those situations whereinthe distance between the target edges (edge marker pulses leading edges)is not less than one-tenth the duration of the horizontal tracking gate.As suggested above, the unit of FIG. 5 has successfully utilizedseparations wherein real and false" edge mark er pulses separated by LSmicroseconds function with a 1.0 microsecond gate pulse G.

FIG. 7 illustrates the effect of the logic section output signal X, onthe positioning of the horizontal tracking gate pulse within each videoscan-line. The first and third line portions indicate situations whereinthe gate pulse has been in effect moved significantly to the left orsignificantly to the right relative to the television picture tuberaster centerlines. In the case of the first line portion (a) of FIG. 7,a large +X, signal will move marker pulse G leftward a proportionaldegree. The second line portion (b) of FIG. 7 shows the positioning ofthe gate pulse G at the horizontal center of the television picture tuberaster essentially by means of delay signal F produced by a zerofeedback input voltage. The zero feedback voltage is used to referenceoperation of the tracker unit to the center of the television raster.FIG. 7(c) illustrates a situation wherein a high negative voltagehorizontal tracking error correction signal is utilized to move thehorizontal tracking gate G toward the extreme right portion of thetelevision camera raster. FIG. 7 also illustrates the relationshipswhich exist between the basic azimuthal tracking gate pulse G, pulseextensions S and T, and the composite pulse U utilized to identifyconcurrent azimuthal tracking for vertical logic section 21.

FIG. 8 illustrates the relations which exist as between concurrencesignal L indicating vertical tracking position and the variablypositioned and sequentially fired gate pulses .l and K that make upsignal L. It should be noted that the leading edge of gate pulse .I iscoincident with the trailing edge of variable duration positioning pulseH. Similarly, the leading edge of gate pulse K is coincident with thetrailing edge of gate pulse J. Pulse signal L is the inverted compositeof pulses J and K and is conducted to horizontal logic section 20 foruse in gating edge marker pulses that are coincident therewith and withthe basic horizontal tracking gate pulse. As previously commented, thetrailing edge of pulse signal H is positioned time-wise from the startof each vertical scan in proportion to the magnitude of the +Y, or Y,,error correction signal that is the output of vertical logic section 21.In the arrangements shown in the drawings, if the Y, signal is of zerovoltage value, the trailing edge of pulse H is normally positioned justslightly above the vertical center of the raster.

FIG. 9 illustrates the various signals which occur within videoprocessor section 19 and the synchronization circuit included as amatter of convenience within horizontal logic section 20. The signals ofthe first line within FIG. 9 detail typical positive transmission videosignals produced by camera unit 11 during scanning of a general trackingproblem. The first (a) and secondlast (e) line portions of signal A inFIG. 9 show a representative background situation; the second (b)through fourth (d) line portions show the effect of a dark target Tpositioned against a comparatively light background. The last lineportion (I) shows the presence ofa vertical blanking pulse; horizontalblanking pulses occur in each of the other line portions at the trailingregion. The horizontal and vertical synchronizing pulses produced bytelevision camera unit 11 appear on the line designated C. Alsosuperimposed on that line are the pulses C and C, used to logicallydetermine the existence of a vertical synchronization I pulse in thecomposite synchronization signal. The'last line of FIG. 9 shows thewaveform H which occurs as the result of detecting a verticalsynchronizing pulse in the composite synchronizing signal. Marker pulsesdetecting each contrast change occurring within a scanline aredesignated D. By appropriate manual or automaticsensitivity control, thenumber and degree of contrast change detected within a typical scan-linemay be varied. A variable amplification function carried out withinvideo amplifier section 31 may be adequate for this purpose. Theresulting rectified and squared real and false edge marker pulses areappropriately designated +E and E in the signal line designated E.

FIG. 10 illustrates typical coincidence relations that exist as between-E and +E target edge marker pulses and horizontal gate pulse G duringautomatic operation of the tracking system. As noted therein (FIG.10(0)), for instance), whenever a +E pulse is singularly coincident witha horizontal tracking gate pulse G, the resulting passed pulse (+M) bytriggering one-shot circuit 51 produces a +N pulse of approximatelyone-line duration; no +M or -N pulses are developed in the samescan-line. Although not shown, in those instances in which a E pulseonly is coincident with horizontal tracking gate pulse G (as duringextreme rightward movement of the selected target relative to the sensorviewing axis), a N tracking error detection pulse is generated withinany one video signal horizontal scanline. In those tracking situationswherein alignment correction is required, a grouping of severalconsecutive N or +N pulses will generally exist within an individualfield scan. Assuming that the duration of vertical gate pulses J and Kare each approximately six scanlines and assuming that the targetessentially extends vertically through the duration of the verticaltracking gates, the resulting groupint may consist of as many as 12consecutive tracking error detection pulses.

FIG. II shows generally similar tracking error detec tion pulsewaveforms +P and P developed within vertical logic section 21. It shouldbe noted that each part of tracking error detection pulse signal isessentially passed through either gate 93 or gate 94 if coincident witheither a vertical tracking gate pulse K or J, respectively. Duringproper alignment of the tracking system sensor viewing axis with theselected target in the automatic mode of system operation, -P and Hpulses will occur in sequential groupings of individual pulses. Assumingthat the time duration of the gates produced by one-shot circuits 98 and99 are each approximately six lines and assuming that the tracker unitis detecting one or both of the target edges so as to develop signal 0in each scan-line, as many as 12 successive P pulses in two differentgroupings may occur.

FIG. 12 shows the typical relations which exist as between -N andinverted +N pulses in the FIG. arrangement and within an individualscan-line. When a single edge marker pulse (real or false) is coincidentwith the basic horizontal tracking gate pulse G, an N pulse is developedand serves to activate the subsequent circuits 91, 92, and 71 to producea usable correction signal of proper polarity and magnitude.

FIG. 13 details the typical error correction signals X, that aredeveloped from intermediate signals 0 in response to tracking errordetection pulses indicating a system requirement for re-alignment of thesensor viewing axis relative to the selected target. The time periodsrepresented by the FIG. 13(a) and (b) combination and by the FIG. 13(0)and (d) combination are each essentially one vertical scan-time or atotal of approximately 525 individual scan-lines in duration. It shouldbe noted from FIG. 13 that a grouping of N pulses indicating that arelatively rightward-moving target leading edge is coincident with thebasic horizontal tracking gate produces negative-going output signals 0and X, that drives the tracking gate rightwardly away from thecoincident target edge and toward the target interior and opposite ortrailing edge. Similarly, a grouping of +N pulses (FIG. l3(c))indicating that a relatively leftward-moving target trailing edge (asmanifested by an associated false" marker pulse) is coincident with thebasic horizontal tracking gate produces positive-going output signals 0and X, that drive the tracking gate leftwardly away from the coincidenttarget edge and toward the target interior and opposite or leading edge.

We claim:

1. In a tracking system tracker unit which develops azimuthal andelevational tracking error correction signals from a television camerasensor video signal, in combination:

a. First pulse generator circuit means generating, in

response to a target edge-like contrast characteristic, detected in thetelevision camera sensor video signal, a pair of marker pulsesspaced-apart in a line of scan of the television camera sensor by a timeinterval,

b. Second pulse generator circuit means generating an elevationaltracking gate pulse having a time duration in a field of scan of thetelevision camera sensor in excess of a line of scan of the televisioncamera sensor for coincidence gating at least one of said pair of markerpulses during concurrent system azimuthal tracking to develop theelevational tracking error correction signal,

c. Third pulse generator circuit means generating an azimuthal trackinggate pulse having a time duration in a line of scan of the televisioncamera sensor less than said marker pulse spacing time interval forcoincidence gating one of said pair of marker pulses on a singularlycoincident basis during concurrent system elevational tracking todevelop the azimuthal tracking error correction signal,

. Fourth pulse generator circuit means generating a pulse extension forsaid azimuthal tracking 'gate pulse in a line of scan of the televisioncamera sensor,

e. AND gate circuit means gating one of said marker pulses coincident intime with said elevational tracking gate pulse and a pulse indicatingconcurrent system azimuthal tracking as a tracking error detection pulsefor developing the elevational tracking error correction signal, and

f. Circuit means combining said azimuthal tracking gate pulse and saidpulse extension into a combination pulse and providing said combinationpulse to said AND gate circuit means as said pulse indicating concurrentsystem azimuthal tracking.

2. The invention defined by claim I, wherein said pulse extensionimmediately precedes said azimuthal tracking gate pulse in time in theline of scan of the television camera sensor.

3. The invention defined by claim 1, wherein said pulse extensionimmediately follows said azimuthal tracking gate pulse in time in theline of scan of the television camera sensor.

4. The invention defined by claim 1, wherein said pulse extension iscomprised of two extension portions that immediately precede andimmediately follow said azimuthal tracking gate pulse in time in theline of scan of the television camera sensor.

5. The invention defined by claim 1, wherein said pulse extension has atime duration in the line of scan of the television camera sensorsubstantially not less than the time duration of one of said markerpulses.

6. The invention defined by claim 4, wherein said two extension portionscomprising said pulse extension each have a time duration in the line ofscan of the television camera sensor substantially not less than thetime duration of either of said marker pulses.

7. In a method of developing azimuthal and elevational tracking errorcorrection signals from a television camera sensor video signal, thesteps of:

a. Generating, in response to a target edge-like contrast characteristicdetected in the television camera sensor video signal, a pair of markerpulses spaced-apart in a line of scan of the television camera sensor bya time interval,

b. Generating an elevational tracking gate pulse having a time durationin a field of scan of the television camera sensor in excess ofa line ofscan of the television camera sensor for coincidence gating at least oneof said pair of marker pulses during con current system azimuthaltracking to develop the elevational tracking error correction signal,

c. Generating an azimuthal tracking gate pulse having a time duration ina line of scan of the television camera sensor less than said markerpulse spacing time interval for coincidence gating said pair of markerpulses on a singularly coincident basis during concurrent systemelevational tracking to develop the azimuthal tracking error correctionsignal,

d. Generating a pulse extension for said azimuthal tracking gate pulsein a line of scan of the televi sion camera sensor, and

e. Gating one of said marker pulses coincident in time with saidelevational tracking gate pulse and with a time comprised of the timeduration of said azimuthal tracking gate pulse and the time duration ofsaid pulse extension as a tracking error detection pulse for developingthe elevational tracking error correction signal.

8. The invention defined by claim 7, wherein said pulse extension isgenerated immediately before said azimuthal tracking gate pulse.

9. The invention defined by claim 7, wherein said pulse extension isgenerated immediately following said azimuthal tracking gate pulse.

10. The invention defined by claim 7, wherein said pulse extension isgenerated in two pulse portions, one of which immediately precedes saidazimuthal tracking gate pulse and the other of which immediately followssaid azimuthal tracking gate pulse.

11. The invention defined by claim 7, wherein said pulse extension has atime duration in the line of scan of the television camera sensorsubstantially not less than the time duration of one of said markerpulses.

12. The invention defined by claim 10, wherein each of said two pulseportions comprising said pulse extension is generated with a timeduration in the line of scan of the television camera sensorsubstantially not less than the time duration of either of said markerpulses.

1. In a tracking system tracker unit which develops azimuthal andelevational tracking error correction signals from a television camerasensor video signal, in combination: a. First pulse generator circuitmeans generating, in response to a target edge-like contrastcharacteristic, detected in the television camera sensor video signal, apair of marker pulses spaced-apart in a line of scan of the televisioncamera sensor by a time interval, b. Second pulse generator circuitmeans generating an elevational tracking gate pulse having a timeduration iN a field of scan of the television camera sensor in excess ofa line of scan of the television camera sensor for coincidence gating atleast one of said pair of marker pulses during concurrent systemazimuthal tracking to develop the elevational tracking error correctionsignal, c. Third pulse generator circuit means generating an azimuthaltracking gate pulse having a time duration in a line of scan of thetelevision camera sensor less than said marker pulse spacing timeinterval for coincidence gating one of said pair of marker pulses on asingularly coincident basis during concurrent system elevationaltracking to develop the azimuthal tracking error correction signal, d.Fourth pulse generator circuit means generating a pulse extension forsaid azimuthal tracking gate pulse in a line of scan of the televisioncamera sensor, e. AND gate circuit means gating one of said markerpulses coincident in time with said elevational tracking gate pulse anda pulse indicating concurrent system azimuthal tracking as a trackingerror detection pulse for developing the elevational tracking errorcorrection signal, and f. Circuit means combining said azimuthaltracking gate pulse and said pulse extension into a combination pulseand providing said combination pulse to said AND gate circuit means assaid pulse indicating concurrent system azimuthal tracking.
 2. Theinvention defined by claim 1, wherein said pulse extension immediatelyprecedes said azimuthal tracking gate pulse in time in the line of scanof the television camera sensor.
 3. The invention defined by claim 1,wherein said pulse extension immediately follows said azimuthal trackinggate pulse in time in the line of scan of the television camera sensor.4. The invention defined by claim 1, wherein said pulse extension iscomprised of two extension portions that immediately precede andimmediately follow said azimuthal tracking gate pulse in time in theline of scan of the television camera sensor.
 5. The invention definedby claim 1, wherein said pulse extension has a time duration in the lineof scan of the television camera sensor substantially not less than thetime duration of one of said marker pulses.
 6. The invention defined byclaim 4, wherein said two extension portions comprising said pulseextension each have a time duration in the line of scan of thetelevision camera sensor substantially not less than the time durationof either of said marker pulses.
 7. In a method of developing azimuthaland elevational tracking error correction signals from a televisioncamera sensor video signal, the steps of: a. Generating, in response toa target edge-like contrast characteristic detected in the televisioncamera sensor video signal, a pair of marker pulses spaced-apart in aline of scan of the television camera sensor by a time interval, b.Generating an elevational tracking gate pulse having a time duration ina field of scan of the television camera sensor in excess of a line ofscan of the television camera sensor for coincidence gating at least oneof said pair of marker pulses during concurrent system azimuthaltracking to develop the elevational tracking error correction signal, c.Generating an azimuthal tracking gate pulse having a time duration in aline of scan of the television camera sensor less than said marker pulsespacing time interval for coincidence gating said pair of marker pulseson a singularly coincident basis during concurrent system elevationaltracking to develop the azimuthal tracking error correction signal, d.Generating a pulse extension for said azimuthal tracking gate pulse in aline of scan of the television camera sensor, and e. Gating one of saidmarker pulses coincident in time with said elevational tracking gatepulse and with a time comprised of the time duration of said azimuthaltracking gate pulse and the time duration of said pulse extension as atracking error detection pulse for developing the elevationAl trackingerror correction signal.
 8. The invention defined by claim 7, whereinsaid pulse extension is generated immediately before said azimuthaltracking gate pulse.
 9. The invention defined by claim 7, wherein saidpulse extension is generated immediately following said azimuthaltracking gate pulse.
 10. The invention defined by claim 7, wherein saidpulse extension is generated in two pulse portions, one of whichimmediately precedes said azimuthal tracking gate pulse and the other ofwhich immediately follows said azimuthal tracking gate pulse.
 11. Theinvention defined by claim 7, wherein said pulse extension has a timeduration in the line of scan of the television camera sensorsubstantially not less than the time duration of one of said markerpulses.
 12. The invention defined by claim 10, wherein each of said twopulse portions comprising said pulse extension is generated with a timeduration in the line of scan of the television camera sensorsubstantially not less than the time duration of either of said markerpulses.